Device for determining the electric potential of the brain

ABSTRACT

A device for determining a physiological or psychological state of a mammal is disclosed. The device has at least one earpiece with a main body having a body of revolution with an axis of revolution, and an endpiece configured to be inserted into an ear canal. The endpiece has a cylindrical channel intended to receive a body of revolution for detachably mounting the endpiece on the main body, the endpiece being arranged to be movable in rotation about the axis of revolution in order to allow at least one electrode to be oriented toward a zone of the brain of the mammal, and the endpiece having a plurality of electrodes arranged on an outer surface of the endpiece, each electrode being configured to pick up an electrical signal in the ear canal of the mammal.

TECHNICAL FIELD

The invention relates to the field of devices for determining aphysiological or psychological state of a mammal, in particular devicesfor determining such a state by measuring an electroencephalogram (EEG)signal.

BACKGROUND ART

An in-the-ear device for measuring biological data of humans is known,such as the one described in US 2018/0235540. This device comprises aninterchangeable part intended to be inserted into an ear canal andprovided on its outer surface with electrodes that are intended todetect an electrical signal originating from the heart. This device alsocomprises a housing on which is mounted an external electrode intendedto receive a user's finger in order to form a reference potential.

The replacement of the interchangeable part of these devices isrestrictive and complex to carry out. Finally, the detection ofelectrical signals by the electrodes may lack precision.

SUMMARY

An underlying concept of this invention is to make available a devicewhich serves for measuring biological data and which is easier tooperate and is more capable of providing more precise signals.

For this purpose, the invention proposes a device making it possible,for example, to determine a physiological or psychological state of amammal.

According to one embodiment, the device comprises at least one earpiececomprising:

-   -   a main body comprising a cylindrical part having an axis of        revolution, and    -   an endpiece configured to be inserted into an ear canal, said        endpiece having a cylindrical channel intended to receive the        cylindrical part for detachably mounting the endpiece on the        main body, the endpiece being arranged to be movable in rotation        about the axis of revolution in order to allow at least one        electrode to be oriented toward a zone of the brain of the        mammal, and said endpiece comprising a plurality of electrodes        arranged on an outer surface of the endpiece, each electrode        being configured to pick up an electrical signal in the ear        canal of the mammal, and said device comprising first electrical        tracks electrically insulated from each other, arranged in the        cylindrical channel of the endpiece and connected to the        electrodes, and second electrical tracks electrically insulated        from each other, arranged in the cylindrical part of the main        body and intended to convey the signal, picked up by the        electrodes, to a calculation means.

According to advantageous embodiments, a device of this kind can haveone or more of the following features.

According to one embodiment, each of the first electrical tracks, oreach of the second electrical tracks, has an annular shape having as itsaxis said axis of revolution and is arranged in electrical contact withone of said first electrical tracks, or one of said second electricaltracks, independently of the orientation of the endpiece about said axisof revolution, and said first or second electrical tracks of annularshape are spaced along said axis of revolution.

Such a device is advantageous in that it makes it possible to remove theendpiece and replace it with another endpiece in any circumferentialorientation, without requiring guide means to ensure the connectionbetween the electrodes and the calculation means. The device is thusless complex to operate. Another advantage of using circular tracks isthat they permit rotation of the electrodes about the axis ofrevolution. The orientation of the endpiece can therefore be easilyadjusted, if necessary, such that one or more of the electrodes isoriented toward a specific zone situated around the ear canal. Thesignals picked up by the electrodes can therefore be more targeted andpermit a more precise determination of the physiological orpsychological state of the mammal.

The electrodes of the device can be made in many ways. According to oneembodiment, at least one electrode has an outer part extending over alongitudinal part, in the direction of the axis of revolution, of theouter surface of the endpiece. According to one embodiment, theelectrodes are spaced apart in a circumferential direction about theaxis of revolution.

According to one embodiment, at least one electrode has a length equalto or slightly less than the length of the endpiece.

According to one embodiment, at least one electrode has an inner partextending over a part of the cylindrical channel in order to form afirst electrical track.

According to one embodiment, the electrodes are spaced apart in acircumferential direction by a constant distance.

According to one embodiment, each of the second electrical tracks isannular, and each of the first electrical tracks is configured to comeinto contact with a respective second annular electrical track.According to one embodiment, the first electrical tracks extend in anarc of a circle on the inner part of the cylindrical channel about theaxis of revolution. According to one embodiment, the first electricaltracks constitute a metallic deposit on the cylindrical channel of theendpiece.

According to another embodiment, each of the first electrical tracks isannular and each of the second electrical tracks forms a contact padconfigured to come into contact with a respective first annularelectrical track. According to one embodiment, the contact pad extendsover an arc of a circle of the cylindrical part of the main body aboutthe axis of revolution. According to an alternative embodiment, thecontact pad has a rectangular, semi-spherical, annular or semi-annularshape. According to one embodiment, the contact pad is a metallicdeposit on the outer surface of the cylindrical part or of the channelof the endpiece.

The endpieces of the device can be made in different configurations.According to one embodiment, the endpiece is made of elastic materialconfigured to adapt to a dimension, in particular a circumference, ofthe ear canal so as to ensure contact between the electrodes and theinner surface of the ear canal.

According to one embodiment, the endpiece comprises a polymer material,and at least one electrode comprises a conductive fabric embedded orrecessed in the polymer material of the endpiece.

According to an alternative embodiment, the endpiece comprises a polymermaterial, and at least one electrode comprises a conductive materialselected from conductive polymers and silicone doped with nanoparticles,embedded or recessed in the polymer material of the endpiece.

According to another embodiment, the endpiece comprises a polymermaterial comprising a plurality of conductive parts electricallyinsulated from one another and forming the electrodes.

According to one embodiment, the device comprises means for locking theendpiece on the cylindrical part of the main body.

According to one embodiment, these locking means comprise a grooveand/or a rib and/or a stop arranged in the cylindrical part of the mainbody and/or in the endpiece.

According to one embodiment, the device comprises a calculation meansconfigured to determine a physiological or psychological state of amammal as a function of the electrical signals picked up by theelectrodes.

According to one embodiment, the device comprises processing meansincluding a measuring device for measuring physical quantities on theelectrical signals picked up by the reference electrode and the at leastone measuring electrode. These physical quantities are, for example, theintensity or the voltage of the signals picked up by the electrodes.

According to one embodiment, the processing means are configured toamplify the electrical signals picked up by the electrodes beforetransmission to the measuring device.

According to one embodiment, this amplification is achieved by means ofan impedance adapter.

According to one embodiment, the plurality of electrodes comprises areference electrode and at least one measuring electrode.

According to one embodiment, the calculation means is configured todetermine the physiological or psychological state as a function of adifference between two electrical signals picked up by two of saidelectrodes of the earpiece, for example of at least one differencebetween the electrical signal picked up by one of the measuringelectrodes and the electrical signal picked up by the referenceelectrode. According to one embodiment, any artefacts present on thesesignals are removed using a multi-channel artefact removal method, forexample independent component analysis. According to one embodiment, thedifference or differences between the electrical signal picked up by oneof the measuring electrodes and the electrical signal picked up by thereference electrode is quantified in the form of a potential difference.According to one embodiment, the calculation means determines thispotential difference from the voltage of the signals that is measured bythe measuring device.

According to one embodiment, the measuring device makes it possible tomeasure physical quantities on the electrical signal picked up by thereference electrode by virtue of at least one first resistor in which acurrent flows that corresponds to a sum between a current correspondingto the electrical signal picked up by the reference electrode and acurrent coming from a reference generator having known characteristics.According to one embodiment, the at least one resistor can be a singleresistor or an electrical assembly made up of several resistors.According to one embodiment, the electrical assembly of severalresistors can be an assembly of resistors in series. The physicalcharacteristics of the electrical signal picked up by the referenceelectrode can be determined by applying Ohm's law to the resistance ifit is unique, or by applying a voltage divider bridge formula if oneconsiders an electrical assembly of resistors. In this embodiment, thevalue of the resistor or resistors used is known.

In one embodiment, the generator is a current generator. In analternative embodiment, the generator is a voltage generator. Thephysical characteristics of the electrical signal that is picked up bythe reference electrode can be determined by applying Ohm's law to theresistance. In one embodiment, the generator supplying the resistordelivers a voltage current that is considerably high (in absolute value)in relation to the voltage variations expected in the signal picked upby the reference electrode. An advantage of this embodiment is theability to detect the presence of aberrant values. This embodiment isadvantageous in particular for calculating a potential differencebetween a signal picked up by a measuring electrode and a signal pickedup by the reference electrode according to the embodiment below.

According to an advantageous embodiment, the measuring device makes itpossible to measure physical quantities on the electrical signal pickedup by the at least one measuring electrode by virtue of at least onesecond resistor in which a current flows that corresponds to a sumbetween a current corresponding to the electrical signal picked up bythe at least one measuring electrode and a current coming from a secondgenerator having known characteristics and delivering a voltage higherthan that delivered by the reference generator. According to oneembodiment, the at least one resistor can be a single resistor or anelectrical assembly made up of several resistors. According to oneembodiment, the electrical assembly of several resistors can be anassembly of resistors in series. The physical characteristics of theelectrical signal picked up by the reference electrode can be determinedby applying Ohm's law to the resistance if it is unique, or by applyinga voltage divider bridge formula if one considers an electrical assemblyof resistors. According to one embodiment, the voltage delivered by thesecond generator is positive and of considerably higher value than thevoltage variations expected in the signal coming from a measuringelectrode.

This advantageous embodiment makes it easy to identify aberrantmeasurements. Indeed, in this embodiment, it is expected that thepotential difference between the voltage of the signal measured by ameasuring electrode and the voltage of the signal measured by thereference electrode will fluctuate little around half the sum of thevoltage supplying the at least one resistor making it possible tomeasure the voltage of the signal picked up by the measuring electrode,and the voltage supplying the at least one resistor making it possibleto measure the voltage of the signal picked up by the referenceelectrode. For example, if the resistor (or the assembly of resistors inseries) for measuring the voltage of the signal picked up by themeasuring electrode is supplied with a voltage of 2.4 V and if theresistor (or the assembly of resistors in series) for measuring thevoltage of the signal picked up by the measuring electrode is suppliedwith a voltage close to 0 V (for example of the order of 0.1 V), and ifthe voltage fluctuation in the signal picked up by the electrodes isexpected around μV, the potential difference obtained must be around 1.2V, with fluctuations of the order of μV. Any measurement that deviatessignificantly from this value, for example by a few mV, will beconsidered as an aberrant value.

According to one embodiment, the plurality of electrodes comprises, inaddition to the reference electrode and the at least one measuringelectrode, a ground electrode. The ground electrode is oriented toward aspecific part of the ear canal, said specific part of the ear canalmaking it possible to pick up a stable signal preferably close to thenoise caused by disturbances outside the body of the mammal. Accordingto one embodiment, the endpiece is formed so as to be able to be incontact with the specific part of the ear canal when it is inserted intothe ear canal, and the ground electrode is located on a part of theendpiece in contact with the specific part of the ear canal in order topick up an electrical signal on said specific part of the ear canal.According to one embodiment, the specific part of the ear canal is amammalian tragus. In the case of a human, the tragus is an ear cartilagelocated at the entrance to the ear canal.

According to one embodiment, the signal picked up by the groundelectrode is used by processing means to effect a noise reduction in thesignals measured by the reference electrode and the at least onemeasuring electrode. According to one embodiment, the noise reduction isachieved by means of a common-mode rejection circuit. This embodiment isadvantageous because it makes it possible to reduce the noiseoriginating from disturbances outside the body of the mammal.

According to one embodiment, the ground electrode is connected to apotential corresponding to half the sum of the voltages delivered by twovoltage generators, for example the two generators of the measuringdevice. This embodiment is advantageous because it makes it possible todefine identically a zero potential in the whole circuit.

According to one embodiment, the processing means comprise a firstresistor connected to a first voltage generator and arranged in such away as to receive the electrical signal picked up by the referenceelectrode, and a second resistor connected to a second voltage generatorand arranged in such a way as to receive the electrical signal picked upby the at least one measuring electrode, the second voltage generatordelivering a voltage greater than that delivered by the first voltagegenerator.

In the embodiment involving a ground electrode, the reference electrodeand the measuring electrodes can be chosen arbitrarily.

According to one embodiment, in particular in the absence of a groundelectrode, one of the electrical signals is an electrical referencesignal; it is preferably a substantially stable electrical signal. Inother words, the reference electrode is defined as the one that picks upa substantially stable electrical signal.

According to one embodiment, the electrical reference signal is measuredby an electrode, namely the reference electrode, which is intended to beoriented toward an osseous part near the ear canal of the mammal. Inparticular, this osseous part is a mastoid.

An advantage of such an arrangement lies in obtaining a stable referencesignal, that is to say one that fluctuates little, without requiring theuse of an electrode external to the endpiece.

According to one embodiment, the endpiece comprises a marking configuredfor visually recognizing the reference electrode. According to oneembodiment, the reference electrode is connected to a predefinedpotential.

According to one embodiment, the predefined potential corresponds tohalf the sum of the voltages delivered by the two aforementioned voltagegenerators. According to one embodiment, the reference electrode thusconnected is placed on the endpiece so as to be in contact with thesurface of the ear canal of the mammal. This embodiment is advantageousbecause it makes it possible to artificially electrify the skin bytransmitting to it the potential to which the reference electrode isconnected (since the reference electrode is connected to a certainpotential and is also affixed to the surface of the ear canal). Thismakes it possible to increase the stability of the signal picked up bythe reference electrode at the surface of the ear canal where it isaffixed. Indeed, it is then expected that the signal coming from thispart of the ear canal will fluctuate slightly around this potential,while being considerably stable.

According to embodiments, the endpiece comprises means for determiningthe electrical reference signal. According to one embodiment, theendpiece comprises a marking, preferably on its outer surface,configured to be directed toward the mastoid of the mammal uponinsertion of the endpiece into the ear canal of the mammal, so that oneof the electrodes is directed toward the mastoid of the mammal. In otherwords, this marking indicates how to orient one of the electrodes towardan osseous part near the ear canal of the mammal, in particular themastoid.

According to an alternative embodiment, the reference signal is detectedautomatically by a selector. In particular, the selector is configuredto receive the electrical signals from the electrodes and to detect areference electrode, said reference electrode being selected as theelectrode emitting the electrical signal having the most stableelectrical potential, that is to say the one having the fewestfluctuations, among the electrical signals picked up by the electrodes.

According to one embodiment, the signal selector is arranged upstream ofthe calculation means and connected to the second electrical tracks.According to one embodiment, the selector is connected to an amplifiercomprising a negative input and at least one positive input, and thesignal selected by the selector is conveyed to the negative input of theamplifier. In particular, the amplifier is connected to the calculationmeans.

According to one embodiment, the selector is composed of a connectionmechanism, for example a reversible connector arranged upstream of theamplifier and of a signal tester arranged downstream of said amplifier.The reversible connector can be adapted to connect each of the secondelectrical tracks to an input of the amplifier, and the signal testercan be configured to determine a sign of the difference(s) between thesignal coming from the at least one positive input and the signal comingfrom the negative input. The selector can be configured to convey thesignals output by the amplifier to the calculation means in response tothe signal tester detecting that all the differences are positive. Theselector can additionally be configured to modify a configuration of thereversible connector so as to connect another of the second tracks tothe negative input of the amplifier in response to the signal testerdetecting at least one negative difference among the differencescalculated. In this embodiment, the most stable electrical signal is theone having the lowest electrical potential.

According to one embodiment, at least one of the electrodes is orientedtoward a temporal lobe of the mammal.

According to one embodiment, the physiological or psychological staterelates to an electrical activity of an organ of the mammal, selectedfrom the group consisting of a brain, a heart, a nerve, a muscle and aneye.

According to one embodiment, the physiological or psychological staterelates to an EEG signal determined by the calculation means from atleast one electrical signal emitted by a zone of the mammal's brain andpicked up by one or more of the electrodes arranged in the ear canal.

According to one embodiment, the physiological or psychological state isfatigue of the mammal, a level of attention of the mammal or anepileptic seizure of the mammal.

According to one embodiment, the psychological state is a pre-ictalactivity of the brain.

According to one embodiment, the device comprises a means for filteringthe electrical signals, said means being configured to attenuateparasitic signals detected by one of said electrodes.

Such parasitic signals may be generated by movements of the mammaland/or of the endpiece in the ear canal and/or may originate from theenvironment of the device.

According to one embodiment, the filtering means comprises a band-passfilter having a pass band between 0.3 Hz and 50 Hz, in particularbetween 1 Hz and 40 Hz.

According to one embodiment, the calculation means is configured to:

determine an electroencephalogram signal of the mammal as a function ofthe electrical signals measured,determine an amplitude of at least one brain wave in a predefinedfrequency range as a function of said electroencephalogram signal, anddetermine a psychological state as a function of said amplitude of atleast one brain wave by comparing said amplitude with a predeterminedthreshold.

One application of the device is the detection of drowsiness in anindividual and the use of this detection to trigger a wake-up for saidindividual.

According to one embodiment, the main body comprises a wired or wirelessdata transmission means configured to communicate with the calculationmeans. The transmission means is configured to transmit the electricalsignals, picked up by the electrodes, to the calculation means.

According to one embodiment, the main body is an electrically insulatinghousing comprising the means for transmitting data to the calculationmeans and the signal processing means.

According to one embodiment, the device comprises a single earpiece.

According to an alternative embodiment, the device comprises twoearpieces. The earpieces are identical or different.

According to a corresponding embodiment, the device comprises twoearpieces configured to be arranged respectively in a first ear canal ofthe mammal and a second ear canal of the mammal and intended to conveyrespective electrical signals to a calculation means. In particular, thecalculation means is intended to determine the physiological orpsychological state as a function of a signal measured by an electrodeof the earpiece arranged in the first ear canal and a signal measured byan electrode of the earpiece arranged in the second ear canal, inparticular as a function of a difference between the two signals.

Thus, in one embodiment, at least one difference between two signalspicked up respectively in the ear canal of a left ear and of a right earof the mammal is exploited.

According to one embodiment, the calculation means is arranged at adistance from the main body.

According to a corresponding embodiment, the device comprises a singlecalculation means.

According to another embodiment, the calculation means is arranged inthe main body of an earpiece.

According to a corresponding embodiment, each earpiece comprises acalculation means.

According to another aspect of the invention, the invention makesavailable a method for producing a device as described above, in whichmethod at least one electrode is partially or entirely obtained bymolding a conductive material, the method comprising a step of molding apolymer in a slide mold in order to form a first solidified component,and a step of molding a liquid or pasty conductive material, preferablyconductive polymer or silicone doped with nanoparticles, in saidsolidified component.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood, and other objects, details,features and advantages thereof will become clearer during the followingdescription of several particular embodiments of the invention, providedsolely by way of non-limiting illustration, with reference to theattached drawings.

FIG. 1 is a side view of a device according to a first embodiment of theinvention.

FIG. 2 is a view of the interior of the device in the plane of FIG. 1.

FIGS. 3a and 3b are a plan view and a three-dimensional sectional view,respectively, of the upper part of an endpiece from FIG. 3a that can beused in the device of FIG. 1.

FIG. 4 is a sectional view of a device according to a second embodimentof the invention.

FIG. 5 is a diagram of means for processing an electrical signal, whichmeans can be used in a device according to one embodiment of theinvention.

FIG. 6 is a diagram of a device according to a third embodiment of theinvention.

FIG. 7 is a diagram of a data processing method that can be implementedby a calculation means of the device according to one embodiment of theinvention.

FIGS. 8a and 8b are diagrams of two embodiments of an automatic signalselector.

FIG. 9 is a perspective view of an endpiece comprising electrodesaccording to another embodiment.

FIG. 10 is a plan view of the endpiece from FIG. 9.

FIG. 11 is an electrical block diagram of an earpiece according to oneembodiment, connected to the brain of the mammal.

FIG. 12 is an electrical block diagram of an earpiece according toanother embodiment, connected to the brain of the mammal.

DESCRIPTION OF THE EMBODIMENTS

FIGS. 1 and 2 show a first embodiment of a device for determining apsychological or physiological state of a mammal, in particular aperson.

The device 100 is provided for determining electroencephalogram (EEG)data of a person. The device 100 comprises an earpiece, for example of ashape and size similar to an earphone, comprising a housing 102 and adetachable endpiece 104.

In FIG. 1, the device is seen from the side, and therefore the partslocated outside of the device are visible, while inner or non-visibleparts are represented by dotted lines. In FIG. 2, the endpiece 104 isshown in section in the plane of FIG. 1, while the other elements areshown from the side. The elements located inside the housing 102 arerepresented by dotted lines. The endpiece 104 comprises a convex partand a cylindrical channel 112. The convex part is folded back over acylindrical channel 112, which is integral with the convex part only inthe upper part, as is shown in FIG. 3b . Thus, an empty space is locatedbetween the cylindrical channel 112 and the outer surface of theendpiece 104.

The endpiece 104 is provided on its outer surface with three electrodes106 ₁, 106 ₂ and 106 ₃ configured to pick up electrical signals in anear canal of the person. The endpiece 104 is a component of revolutionabout an axis of revolution 108, and the electrodes are arrangedequidistant from each other in a circumferential direction of theendpiece 104. The endpiece 104 is made of insulating material, forexample silicone, and the electrodes 106 are for example pieces ofconductive fabric embedded in the silicone of the endpiece 104, forexample by gluing.

The dimensions of the endpiece 104 are configured to adapt to the earcanal. In addition, since the endpiece 104 is made of silicone, theelectrodes 106 are kept in contact with an inner wall of the ear canalby virtue of the elasticity of the silicone. The endpiece 104 has alength of between 15 mm and 25 mm and a diameter greater than thediameter of the ear canal, in particular by a percentage of between 2%and 5% of the diameter of the ear canal.

The housing 102 comprises processing means 114 configured to receive theelectrical signals picked up by the electrodes 106, process thesesignals and transform them into digital signals. The processing means114 are connected to a calculation means 115, which can be integrated inthe housing 102 or separate from the latter, in order to determine EEGdata as a function of the signals processed by the processing means 114.

In another embodiment, the processing means 114 can also be arrangedoutside the housing 102.

The housing 102 also comprises a shaft 110 extending from the housing102 and having as its axis the axis of revolution 108. The shaft 110 isconfigured to receive the cylindrical channel 112 formed in the endpiece104. The shaft 110 is provided with three annular electrical tracks 116₁, 116 ₂ and 116 ₃ respectively connected to the electrodes 106 ₁, 106 ₂and 106 ₃. The annular tracks 116 have as their axis the axis ofrevolution 108, and they are arranged at a distance from each other inthe direction of the axis of revolution 108. The shaft 110 is made ofinsulating material, and the electrical tracks 116 are formed by a metaldeposit on the shaft 110. The annular tracks 110 are connected to theprocessing means 114 by electric wires arranged inside the shaft 110.Each of the annular tracks 116 ₁ and 116 ₃ is connected to an electrode106 ₁ and 106 ₃ by first electrical tracks 118 ₁ and 118 ₃ (theelectrical track connecting electrode 106 ₂ to annular track 116 ₂ isnot shown in FIGS. 1 and 2).

In FIGS. 3a and 3b , the endpiece 104 is shown, respectively, in a topview and in a three-dimensional view along section A-A.

The electrodes 106 extend over the entire length of endpiece 104 in thedirection of axis of revolution 108. Moreover, the electrodes 106 aredistributed on the outer surface of the endpiece 104 equidistantly aboutthe axis of revolution 108. In particular, the electrodes 106 extendover an outer surface of the endpiece of about 75%, between 50% and 80%of the total outer surface of the endpiece 104. Other distributions ofthe surface of the electrodes would also be possible.

The first electrical tracks 118 are arranged in the endpiece 104according to an embodiment shown in FIG. 3b . The upper part of theendpiece 104 has been shown in section there along the axis A of FIG. 3a, so that only two electrodes 106 ₁ and 106 ₂ and two first electricaltracks 118 ₁ and 118 ₂ are shown. The endpiece 104 shown in this figureis produced using a slide mold, which makes it possible to obtain threehollow parts on the convex surface of the endpiece 104, said parts beingintended to receive the electrodes 106, these hollow parts eachextending in the form of an initially empty well inside the insulatingpart of the endpiece 104. FIG. 3b shows the wells 121 ₁ and 121 ₂,composed of a vertical portion extending along a longitudinal part ofthe cylindrical channel 112 and of a horizontal portion extending in anarc of a circle, and intended to receive the electrical tracks 118 ₁ and118 ₂. After molding and solidification of the insulating part, a liquidconductive material is poured into each of these wells 121, thus formingthe first electrical tracks 118 ₁, 118 ₂ and 118 ₃, each electricaltrack then occupying a well 121. The liquid conductive material ispoured into the wells until they overflow to fill the hollows on thesurface of the convex part of the endpiece. The liquid conductivematerial, having overflowed into the hollows, then solidifies to formthe electrodes 106. Since there is no contact between the differenthollows and the different wells 121, the respective electricalinsulation of the electrodes 106 and of the electrical tracks 118 castinside is ensured.

Moreover, the cylindrical channel 112 of the endpiece 104 has, on itsinner surface, a shoulder 120 shown in FIG. 3b . This serves to hold theendpiece on the shaft 110. In one embodiment, this shoulder 120 may beabsent.

In another embodiment, not shown in the figures, the first electricaltracks 118 ₁, 118 ₂ and 118 ₃ are contact pads connected to theelectrodes 106 by electrically insulated electrical wires embedded inthe surface of the convex part of the endpiece 104 and on the innersurface of the cylindrical channel 112.

In particular, the shaft 110 has a diameter slightly smaller than thediameter of the cylindrical channel 112 of the endpiece 104, for examplesmaller by a value of between 0.5 mm and 2 mm.

As the first electrical tracks 118 are arranged opposite the annulartracks 116, the endpiece 104 is capable of being rotated about the axisof revolution 108 without risk of interrupting the electrical connectionbetween the electrodes 116 and the processing means 114. Moreover,replacement of the endpiece 104 is thereby facilitated, since there isno need to resort to guide means to provide the electrical connectionwhen mounting the endpiece 104 on the shaft 110.

FIG. 4 shows a view similar to FIG. 2 according to a second embodiment.Unlike the device 100, the device 200 of FIG. 4 comprises a solidendpiece 220, with a cylindrical channel 112 hollowed out inside thelatter. The solid endpiece 220 further comprises three first annularelectrical tracks 202 ₁, 202 ₂ and 202 ₃ arranged in the cylindricalchannel 112 and connected to the electrodes 106 ₁, 106 ₂ and 106 ₃,respectively, by electric wires electrically insulated from one anotherand embedded in the endpiece 220, between its surface and thecylindrical channel 112.

The shaft 110 is provided with three non-annular electrical tracks 204₁, 204 ₂ and 204 ₃ spaced apart in the direction of the axis ofrevolution 108. The non-annular electrical tracks are formed by a metaldeposit extending for example according to a semicircle of the shaftaround the axis of revolution 108 and projecting in the direction of thesolid endpiece 220. The non-annular electrical tracks 204 are arrangedfacing the annular electrical tracks 202 so as to maintain electricalcontact with them.

The shaft 110 has a groove 208 arranged on the side of the housing 102and configured to receive a collar 206 provided in the cylindricalchannel 112 of the endpiece 104. This arrangement makes it possible toblock the translation of the solid endpiece 220 in the direction of theaxis of revolution 108. The shaft 110 also comprises a stop 210 having adiameter greater than the diameter of the shaft 110, so as to keep theendpiece clamped against the stop 210 in order to stabilize its positionin rotation.

FIG. 5 shows processing means 114 that can be used in the device 100 or200.

The processing means 114 are configured to receive one or moreelectrical signals picked up by the electrodes 106. The processing means114 comprise an amplifier 302 provided to amplify the amplitude of theor each electrical signal. The gain of the amplifier 302 can be between12 times and 1000 times. In particular, the processing means 114comprise a preamplifier (not shown in FIG. 5). The amplifier 302 isconnected to an analog/digital converter (ADC) 304 configured todigitize the or each electrical signal. The ADC 304 is connected to adigital signal processing module 306 configured to attenuate anyparasitic signals picked up by the electrodes. These parasitic signalsmay be due to the movement of the person's head, to a movement of theelectrical wires connected to the device, or to the environment of thedevice. This digital signal processing module 306 comprises inparticular a band-pass filter, but also signal-processing functions, inparticular a function for removing the linear component of the signal.This linear component is present on account of choosing a referenceelectrode inside the ear canal without using a mass located outside theear canal. The bandwidth of the band-pass filter 306 is furtherconfigured to select electrical signals originating from a predeterminedorgan, particularly the brain. For example, the pass band of theband-pass filter 306 is between 0.3 Hz and 50 Hz, in particular between1 Hz and 40 Hz. The band-pass filter 306 is connected to a communicationmodule 308 configured to transmit the signals, digitized by the ADC 304and filtered by the band-pass filter 306, to the calculation means 115,either by wire or wirelessly. The digital signal processing module canalso comprise other filters, for example a band-stop filter or notchfilter.

The calculation means 115 of the device 100 or 200 is configured todetermine an electroencephalogram (EEG) signal as a function of theelectrical signals picked up by the electrodes 106, in particular adifference between said electrical signals. The calculation means 115 isconfigured to determine an EEG signal from one of the combinations oftwo electrodes among the electrodes: 106 ₁, 106 ₂ and 106 ₃. One of theelectrodes is chosen as the reference electrode, against which thepotential will be calculated. The brain potential is calculated bytaking the difference between the signals picked up by the otherelectrodes and the signal picked up by the reference electrode. Despitehaving carried out a first processing of the digital signal in order toeliminate the parasitic signals, for example by having chosen by way ofthe filter described above a frequency corresponding to the brain waves,artefacts may still be present on the signals. If there are any ofthese, they are identified by comparing the differences in the signalsfrom the other two electrodes with the reference electrode. Indeed, thetwo signals then present the same parasitic components. In particular,this comparison is carried out by means of a multi-channel artefactsuppression method, preferably independent component analysis.

The choice of the reference electrode is made upstream of thecalculation means, according to the following three examples.

In a first example, the reference electrode is identified by means of amarking on the endpiece 104, making it possible to position the latterin the direction of an osseous part of the mammal, for example amastoid, so as to optimize the stability of the signal, i.e. minimizeits fluctuations, in order to obtain a substantially stable signal whichcan then be used as a reference signal to determine an EEG signal of themammal.

In the other two examples, shown in FIGS. 8a and 8b , an automaticsignal selector makes it possible to determine the reference signal.

In a second example, the reference signal is chosen by means of a signalselector 310 placed upstream of the amplifier 302, said selector 310selecting the most stable signal, that is to say the one that has thefewest fluctuations. The amplifier 302 has one negative input and twopositive inputs, the negative input being intended to receive thereference signal. The signal selected as being the most stable is thenconveyed to the negative input of the amplifier 302. Thus, the moststable signal is identified and can be used as a reference forcalculating the brain potential.

In a third example, the second electrical tracks 118, 204 are connectedto the amplifier 302 by way of a connection mechanism 311, which makesit possible to choose the electrical track that is to be connected toeach input of the amplifier 302. As in the preceding example, theamplifier 302 has one negative input and two positive inputs. Theselector consists of a connection mechanism 311, for example areversible connector, and a signal tester 312 placed downstream of theamplifier 302. The signal tester 312 is configured to determine thesigns of the potential differences between the signals coming from thepositive inputs of the amplifier and the signal coming from the negativeinput, which is then temporarily chosen as reference. The signal chosenfor the negative input must be the one with the lowest potential,because it constitutes the potential reference. However, the lowestpotential is assumed to coincide with the most stable signal. If thesignal tester 312 determines that the potential differences between thesignals coming from the positive inputs of the amplifier and the signalcoming from the negative input are all positive, the signal chosen forthe negative input is indeed the most stable, and the signals at theoutput of the amplifier can then be conveyed to the calculating means115 (first passing through the rest of the processing means 114). Thesignal coming from the negative input of the amplifier will be chosen asthe potential reference. Otherwise, if at least one of the differencesis negative, this means that the signal chosen for the negative inputwas not the one with the lowest potential. In this case, a feedback loopsends a signal to the connection mechanism 311, which modifies the inputconnections of the amplifier 302, and then the test is performed againby the signal tester. The connections are thus modified and the testcarried out until the correct configuration is found, that is to say theconfiguration in which the calculated differences are all positive.

For example, if the electrode chosen as a reference, manually, accordingto the first example set out above, or automatically, according toeither of the second and third examples set out below, is the electrode106 ₃, the EEG signal can thus be obtained from signals detected by theelectrodes 106 ₁ and 106 ₃ or the electrodes 106 ₂ and 106 ₃.

The earpiece described above can be used alone or in combination with asecond earpiece.

Thus, the device 400 of FIG. 6 comprises two earpieces 402 and 402′,similar to the earpiece of the device 100 or 200. Each earpiece 402 and402′ is provided with an endpiece 104 and 104′ similar to the endpieceof the device 100 or 200. Each endpiece 104 and 104′ is arranged in anear canal 404 and 404′ of the person wearing the device 400. Unlike thedevices 100 and 200, the calculation means 115 is arranged at a distancefrom the earpieces 402, and the processing means 114 transmit theelectrical signals, received by the electrodes 106, wirelessly to thecalculation means 115. The calculation means 115 can also beincorporated in one of the two earpieces.

The endpieces 104 are made of elastic material and dimensioned to ensurecontact between the wall of the ear canals and the electrodes 106 and106′ of the endpieces 104 and 104′, respectively.

The calculation means 115 is configured to determine anelectroencephalogram (EEG) signal as a function of the electricalsignals picked up by a combination of two electrodes chosen from thefollowing combinations: 106 ₁ and 106′₃, 106 ₂ and 106′₃, 106 ₃ and106′₃, 106′₁, and 106′₃, 106′₂ and 106′₃. In particular, the EEG signalis determined by a difference between the two signals in combination. Asin the case of operation with one earpiece, artefacts still present inthe signal are removed by means of a multi-channel artefact removalmethod, preferably by independent component analysis.

In this embodiment with two earpieces, the reference electrode is chosenaccording to one of the examples presented in the mode of operation withone earpiece. For example, if the chosen reference electrodes are 106₃and 106′₃, the EEG signal can thus be obtained from signals detected byone of the following combinations of electrodes: 106 ₁ and 106 ₃, 106 ₂and 106 ₃, 106′₁, and 106′₃, 106′₂ and 106′₃, 106 ₁ and 106′₃, 106 ₂ and106′₃, 106′₁, and 106 ₃, and 106′₂ and 106 ₃.

FIG. 7 shows the steps performed by the calculation means 115 of thedevice 100, 200 or 400 in order to determine a level of attention of theperson wearing the device 100, 200 or 400.

The calculation means 115 is configured to perform:

a step 502 for determining an EEG signal as a function of the differencebetween two signals picked up by two electrodes of the same earpiece orof two earpieces,a step 504 for determining a brain wave as a function of the frequencyof the EEG signal. By way of example, if the frequency of the signal isbetween 5 Hz and 15 Hz, in particular equal to 10 Hz, the brain wave isof the α type, and, if the frequency of the signal is between 15 Hz and25 Hz, in particular equal to 20 Hz, the brain wave is of the β type.The brain wave can be determined by any signal processing means, inparticular by applying a Fourier transform,a step 506 for determining a level of attention as a function of thebrain wave. In particular, the level of attention is determined as afunction of the amplitude of the brain wave or of the ratio between twoamplitudes of two brain waves. By way of example, for a brain wave ofthe α type, the calculation means 115 determines that the person lacksattention for an amplitude of the α wave below a first predeterminedthreshold. For a brain wave of the β type, the calculation means 115determines that the person lacks attention for an amplitude of the βwave below a second predetermined threshold. In particular, thecalculation means 115 determines the level of attention by comparing theratio of amplitudes of the α and β waves to a third predeterminedthreshold.

In one embodiment, the calculation means 115 can comprise a step oftriggering a wake-up signal intended to wake the person wearing thedevice 100, 200 or 400.

Moreover, when replacing the endpiece 104, the new endpieces 104 can bemounted in any orientation or a predetermined orientation about the axisof revolution. The electrical connection between the electrodes 106 andthe calculation means 115 is provided by the annular tracks 118 or 202,regardless of the orientation of the endpieces relative to the shaft110.

FIGS. 9 and 10 show an embodiment of an endpiece 700 that has threeelectrodes and can be used in the aforementioned devices 100, 200 and400. The electrodes 702 and 703, arranged diametrically opposite oneither side of the cylindrical part of the endpiece, correspond to ameasuring electrode and a reference electrode. The electrode 701, placedfarther back in relation to the other two, corresponds to a groundelectrode. Its set-back position in relation to the other electrodesallows it to be in contact with the tragus. This is made possible by theconvex shape of the endpiece in the part that will be nearest theentrance to the ear canal. Thus, the three electrodes 701, 702 and 703can be used to perform a measurement, as will be described below withreference to FIG. 11.

It is possible to carry out several parallel recordings in order toincrease the accuracy of the measurement. Each additional recordingrequires an additional electrode (which will be a measuring electrode).To perform two recordings, it is thus possible to add a measuringelectrode on the cylindrical part spaced apart in a circumferentialdirection with respect to the electrodes 702 and 703.

FIG. 11 shows a block diagram of the functioning of the device providedwith the endpiece 700 when it is in use, in contact with the body 630 ofa living mammal. The figure shows in particular the electrical circuitmaking it possible to measure a potential difference between the signalpicked up by a measuring electrode and the signal picked up by areference electrode. The signals originate from the mammalian brain 600.The mammal can be a human, for example.

In FIG. 11, the body 630 is modeled as follows. The mammalian brain 600is modeled as a voltage generator with internal resistances. The voltagegenerated is of the order of 100 μV. The internal resistances here aremade up of the resistance of the head of the individual 601 and theresistance of the skin of the individual 602. The resistance of the skinof the individual 602 is the most important resistance. This resistancevaries between 5 and 100 MΩ. This resistance depends on several more orless controllable parameters. The body 630 also comprises sources ofnoise. These sources of noise are the electrical generators of the body(facial muscles, eyes, etc.), but also external disturbances which caninject current from time to time into the circuit. The generators ofinternal noise are modeled by the internal noise generator 608, and thenoise sources external to the individual are modeled by the externalnoise generator 609. The individual's body then acts as an antenna,which can be modeled by a capacitor 610, of variable capacitancedepending on the current injected by the external noise generator 609.

In order to determine a physiological or psychological state of theindividual, it is necessary to measure a potential difference in thebrain 600, that is to say in this instance between the positive andnegative terminals of the generator that models the brain. A measuringelectrode 702 picks up an electrical signal at the positive terminal,and a reference electrode 703 picks up an electrical signal at thenegative terminal. The voltages of the two signals are influenced by theresistances of the individual's head 601 and skin 602, as is shown inthe diagram. Each of these signals is conveyed to a measuring device 620included in the aforementioned processing means 114.

Before arriving at the measuring device 620, each of the two signals isamplified by passing through an impedance adapter 603, which permits 10to 12 times amplification. The voltage of the current coming from theamplifier is therefore of the order of 10 to 100 μV, while the initialsignal has a potential of the order of μV. To measure the voltage of thesignal picked up by the measuring electrode 702 and by the referenceelectrode 703, the measuring device 620 comprises an internal resistance604, 605, respectively, of a known identical resistance value (inpractice close to 1 GΩ). According to one embodiment, the resistance canbe a set of resistors connected in series. The measurement is carriedout according to the principle of a voltmeter. This resistor isconnected to a voltage generator 606 generating a potential Vm+ and avoltage generator 607 generating a potential Vm−. In practice, a valuechosen for the potentials is for example Vm+=2.4 V and Vm−=0 V. Thesignals thus measured are then conveyed to an operational amplifier 612.The measuring device 620 can be produced by means of an ADS 1292component available from the company Texas Instrument.

This circuit makes it possible to detect the aberrant values during themeasurement of the potential difference between the + and − terminals ofthe generator that models the brain 600. Indeed, the measured potentialdifference must then fluctuate within 10 or 100 μV around 1.2V. Apotential difference that deviates significantly from this value is thendeclared as aberrant. The impedance adapter 603 also makes it possibleto limit the aberrant measurements. Indeed, if one of the signalsobtained exceeds the window of values between Vm− and Vm+, the impedanceadapter 603 does not amplify the signal, and so the measurement isdirectly detected as being aberrant.

When calculating the potential difference, it is also necessary toremove the noise from the measurement. In the embodiment shown in FIG.11, the ground electrode 701 is used to suppress the noise from thenoise sources external to the individual, which are represented bygenerator 609. The solution for suppressing the noise is a common-moderejection circuit 621. For this, the ground electrode 701 is connectedto the midpoint 611 between the resistances 604 and 605.

In the modeling adopted, the effect of this connection is toshort-circuit the capacitor 610 by injecting into the circuit a currentidentical to that generated by the external noise generator 609. Thiscurrent corresponds to the signal picked up by the ground electrode 701in contact with a very stable zone of the ear canal, in which theelectrical signal variations correspond to the variations in externalnoise. An example of a stable zone of this kind, which is able tocapture the purest possible external noise, is the tragus, a cartilagelocated in the ear at the entrance to the ear canal. In practice, thecommon-mode rejection circuit 621 is implemented by connecting theground electrode 701 to a potential corresponding to half the sum of Vm+and Vm−, so that the zero potential is defined in the same way in thewhole circuit. In FIG. 11, it is the midpoint 611 that corresponds tothis potential.

Indeed, it is necessary that the zero potential corresponding to thecurrent permitting noise reduction is the same potential around whichthe measured potential difference fluctuates. With the values givenabove, the potential difference fluctuates around 1.2V, and so theground electrode 701 must be connected to this potential of 1.2V.

In the embodiment in FIG. 12, the plurality of electrodes 106 comprisesonly a measuring electrode 702 and a reference electrode 703. The groundelectrode 701 is omitted. The noise from the generator 609 is suppressedby connecting the reference electrode 703 to the midpoint 611corresponding to half the sum of Vm+ and Vm−. In this embodiment,everything happens as if there were a virtual ground electrode combinedwith the reference electrode 703.

The uses of such a device 100, 200 or 400 are numerous, especially inmedicine, especially for the monitoring of patients with neuronaldiseases, including epilepsy, the screening and diagnosis of neuronaldiseases, the screening and monitoring of children with attentiondisorders, but also for the monitoring of certain professionals, inparticular the monitoring of air traffic controllers or air pilots, themonitoring of sportsmen and women, or for improving daily life, forexample the development of wellness applications.

Although the invention has been described in relation to severalparticular embodiments, it is quite obvious that it is in no way limitedthereto and that it encompasses all the technical equivalents of themeans described and their combinations, provided that the latter fallwithin the context of the invention.

The use of the verb “have”, “comprise” or “include” and its conjugatedforms does not preclude the presence of elements or steps other thanthose stated in a claim.

In the claims, any reference sign between parentheses should not beinterpreted as limiting the claim.

1. A device (100, 200, 400) for determining a physiological orpsychological state of a mammal, the device (100, 200, 400) comprisingat least one earpiece (402) comprising: a main body (102) comprising abody of revolution (110) having an axis of revolution (108), and anendpiece (104, 220, 700) configured to be inserted into an ear canal(404), said endpiece (104, 220) having a cylindrical channel (112)intended to receive the body of revolution (110) for detachably mountingthe endpiece (104, 220) on the main body (102), the endpiece (104, 220)being arranged to be movable in rotation about the axis of revolution(108) in order to allow at least one electrode (106) to be orientedtoward a zone of the brain of the mammal, and said endpiece (104, 220)comprising a plurality of electrodes (106; 701-703) arranged on an outersurface of the endpiece (104, 220), each electrode (106; 701-703) beingconfigured to pick up an electrical signal in the ear canal of themammal, and said device comprising first electrical tracks (118, 202)electrically insulated from each other, arranged in the cylindricalchannel (112) of the endpiece (104, 220) and connected to the electrodes(106), and second electrical tracks (116, 204) electrically insulatedfrom each other, arranged in the cylindrical part (110) of the main body(102) and intended to convey the electrical signal, picked up by theelectrodes (106), to a calculation means (115), in which each of thefirst electrical tracks, or each of the second electrical tracks, has anannular shape having as its axis said axis of revolution and is arrangedin electrical contact with one of said first electrical tracks (118,202), or one of said second electrical tracks, independently of theorientation of the endpiece about said axis of revolution, and saidfirst electrical tracks (118, 202) or second electrical tracks (116,204) of annular shape being spaced along said axis of revolution (108).2. The device (100, 200, 400) as claimed in claim 1, in which at leastone electrode (106) has an outer part extending over a longitudinalpart, in the direction of the axis of revolution (108), of the outersurface of the endpiece (104, 220).
 3. The device (100, 200, 400) asclaimed in claim 1, in which at least one electrode (106) has an innerpart extending over a part of the cylindrical channel (112) in order toform a first electrical track.
 4. The device (100) as claimed in claim1, in which each of the second electrical tracks (116) is annular, andeach of the first electrical tracks (118) is configured to come intocontact with a respective second annular electrical track (116).
 5. Thedevice (100) as claimed in claim 4, in which each of the firstelectrical tracks (118) extends in an arc of a circle on the inner partof the cylindrical channel (112) about the axis of revolution (108). 6.The device (200) as claimed in claim 1, in which each of the firstelectrical tracks (202) is annular, and each of the second electricaltracks (204) forms a contact pad configured to come into contact with arespective first annular electrical track.
 7. The device (400) asclaimed in claim 1, in which the device (400) comprises two earpieces(402, 402′) configured to be arranged in a first mammalian ear canal(404) and a second mammalian ear canal (404′), respectively, andintended to convey respective electrical signals to the calculationmeans (115), said calculation means (115) being suitable for determiningthe physiological or psychological state as a function of a signalpicked up by an electrode (106) of the earpiece (402) arranged in thefirst ear canal (404) and a signal measured by an electrode (106′) ofthe earpiece (402′) arranged in the second ear canal (404′), inparticular as a function of a difference between the two signals.
 8. Thedevice (100, 200, 400) as claimed in claim 1, in which the devicecomprises a calculation means (115) configured to determine aphysiological or psychological state of a mammal as a function of theelectrical signals picked up by the electrodes (106).
 9. The device(100, 200, 400) as claimed in claim 8, in which the plurality ofelectrodes (106) comprises a reference electrode (703) and at least onemeasuring electrode (702), and in which the calculation means (115) isconfigured to determine the physiological or psychological state as afunction of at least one difference between the electrical signal pickedup by one of the measuring electrodes (702) and the electrical signalpicked up by the reference electrode (703).
 10. The device (100, 200,400) as claimed in claim 9, in which the plurality of electrodescomprises, in addition to the reference electrode (703) and the at leastone measuring electrode (702), a ground electrode (701), said groundelectrode being oriented toward a specific part of the ear canal, saidspecific part of the ear canal making it possible to pick up a stablesignal.
 11. The device (100, 200, 400) as claimed in claim 10, in whichthe endpiece (104, 220, 700) is constructed so as to be able to be incontact with the specific part of the ear canal when inserted into theear canal, and in which the ground electrode (701) is located on a partof the endpiece (104, 220, 700) in contact with the specific part of theear canal, in order to pick up an electrical signal on said specificpart of the ear canal.
 12. The device (100, 200, 400) as claimed inclaim 10, in which the specific part of the ear canal is a mammaliantragus.
 13. The device (100, 200, 400) as claimed in claim 10, in whichprocessing means (114, 620) use the signal picked up by the groundelectrode (701) to effect a noise reduction in the signals measured bythe reference electrode (703) and the at least one measuring electrode(702).
 14. The device (100, 200, 400) as claimed in claim 13, in whichthe noise reduction is achieved by means of a common-mode rejectioncircuit (621).
 15. The device (100, 200, 400) as claimed in claim 13, inwhich the processing means comprise two voltage generators (606, 607),and the ground electrode (701) is connected to a potential correspondingto half the sum of the voltages delivered by the two voltage generators(606, 607).
 16. The device (100, 200, 400) as claimed in claim 15, inwhich the processing means comprise a first resistor (605) connected toa first voltage generator (607) and arranged in such a way as to receivethe electrical signal picked up by the reference electrode, and a secondresistor (604) connected to a second voltage generator (606) andarranged in such a way as to receive the electrical signal picked up bythe at least one measuring electrode, the second voltage generatordelivering a voltage greater than that delivered by the first voltagegenerator.
 17. The device (100, 200, 400) as claimed in claim 9, inwhich the electrodes (106, 702, 703) are spaced apart from each other ina circumferential direction about the axis of revolution (108).
 18. Thedevice (100, 200, 400) as claimed in claim 9, additionally comprisingprocessing means (114, 620) including two voltage generators (606, 607),and in which the reference electrode (703) is connected to a potentialcorresponding to half the sum of the voltages delivered by the twovoltage generators (606, 607).
 19. The device (100, 200, 400) as claimedin claim 18, in which the reference electrode is intended to be orientedtoward a mastoid of the mammal upon insertion of the endpiece into theear canal of the mammal.
 20. The device (100, 200, 400) as claimed inclaim 18, in which the endpiece (104, 220) has a marking configured forvisually recognizing the reference electrode.
 21. The device (100, 200,400) as claimed in claim 1, comprising a selector configured to receivethe electrical signals from the electrodes, said selector beingconfigured to detect a reference electrode, among the electrodes (106),said reference electrode being selected as the electrode emitting theelectrical signal having the most stable electrical potential among theelectrical signals picked up by the electrodes (106).
 22. The device(100, 200, 400) as claimed in claim 1, in which the endpiece (104, 220)comprises a polymer material, and at least one electrode (106) comprisesa conductive fabric embedded or recessed in the polymer material of theendpiece.
 23. The device (100, 200, 400) as claimed in claim 1, in whichthe endpiece (104, 220) comprises a polymer material, and at least oneelectrode (106) comprises a conductive material selected from conductivepolymers and silicone doped with nanoparticles, embedded or recessed inthe polymer material of the endpiece.
 24. The device (100, 200, 400) asclaimed in claim 1, in which the main body (102) comprises wired orwireless data transmission means (308) configured to communicate withthe calculation means (115).
 25. The device (100, 200, 400) as claimedin claim 1, in which the device comprises a means for filtering theelectrical signals, said means being configured to attenuate parasiticsignals detected by one or more of said electrodes.
 26. The device (100,200, 400) as claimed in claim 25, in which the filtering means comprisesa band-pass filter (306) having a pass band between 0.3 Hz and 50 Hz, inparticular between 1 Hz and 40 Hz.
 27. The device (100, 200, 400) asclaimed in claim 1, in which the calculation means is configured to:determine an electroencephalogram signal of the mammal as a function ofthe electrical signals measured, determine an amplitude of at least onebrain wave in a predefined frequency range as a function of saidelectroencephalogram signal, and determine a psychological state as afunction of said amplitude of at least one brain wave by comparing saidamplitude with a predetermined threshold.
 28. The device (100, 200, 400)as claimed in claim 1, in which the physiological or psychological staterelates to an electrical activity of an organ of the mammal, selectedfrom the group consisting of a brain, a heart, a nerve, a muscle and aneye.
 29. The device (100, 200, 400) as claimed in claim 1, in which thephysiological or psychological state is mammalian fatigue, a mammalianattention level or a mammalian epileptic seizure.